The present invention relates generally to an improved rope structure, and more specifically to a composite rope structure having a core consisting primarily of high modulus fibers, and a sheath consisting primarily of a relatively lower modulus fiber having high abrasion resistance.
The fibers comprising the core are, as indicated, primarily high modulus fibers while the fibers comprising the sheath are relatively lower modulus fibers having high abrasion resistance. The composite structure has been found to provide a finished product having properties which exceed the sum of the individual parts, thereby providing and contributing to a synergistic effect in the overall finished product.
In the preparation of ropes or lines, the utilization of high modulus fibers alone normally provides two disadvantages, the first being the high specific gravity of these fibers, the second being the generally low abrasion resistance. For certain applications, such as utilization as a water ski-tow rope, the use of high modulus fibers may provide a finished product with a specific gravity greater than 1.0, thereby having a non-floating line. Furthermore, the low abrasion resistance of these fibers limits or restricts the application of the finished line for a wide variety of uses.
The utilization of lower modulus fibers will, of course, provide a specific gravity normally less than 1, however the stretch characteristics of such fibers when braided into a line also limits the application of the braided product. In the present structure, a high modulus core is covered with a sheath of a different fiber having high abrasion resistance and low specific gravity, thereby achieving a finished rope product with a specific gravity less than 1, and having high strength and low stretch.
The core material is preferably prepared from fibers which consist essentially of a polyimide of an aromatic tetracarboxylic acid dianhydride having the recurring unit with the structural formula: ##EQU1## wherein R is a tetravalent aromatic radical, and wherein R is a divalent benzenoid radical. Fibers of such polyimide materials are co-mercially available. The sheath material, as indicated, consists primarily of filaments of a polyolefin selected from the group consisting of polypropylene and polyethylene. Such polyolefin filaments are, of course, commercially available.
Therefore, it is a primary object of the present invention to provide an improved composite rope structure having low stretch, high strength, and high abrasion resistance.
It is a further object of the present invention to provide an improved braided rope structure which comprises a blend of filaments braided together to form the composite line structure, and including a braided core of filaments having a high modulus and a sheath braided thereover, the sheath comprising filaments of lower modulus, but significantly higher abrasion resistance.
It is a further object of the present invention to provide an improved rope comprising a plurality of discreet filaments, the filaments being arranged in a core and sheath structure, the composite of which forms a high strength core and a high abrasion resistance sheath, and with the composite structure having high strength and low stretch characteristics.
Other further objects of the present invention will become apparent to those skilled in the art upon a study of the following specification, appended claims and accompanying drawings.